This invention pertains generally to phased array antennas using a plurality of radiating elements and particularly to antennas of such type wherein collimation and steering of a beam of electromagnetic energy is accomplished by controlling phase shifters in circuit with the radiating elements.
It is known in the art that the efficacy of a steerable phased array antenna under field conditions is largely dependent upon the characteristics of the phase shifters incorporated in such an antenna. That is to say, whether ferrite or diode phase shifters are used, variations between such devices due to different ambient temperatures and operating frequencies and to manufacturing tolerances combine to limit the accuracy of collimation and steering.
It has long been customary to select phase shifters for an array and then to compensate for manufacturing tolerances by "trimming" whereby the electrical length of the transmission line to each radiating element is adjusted. Such a compensation then is effective to optimize operation under a predetermined condition, but is not effective when changes in temperature or frequency are experienced. In addition, because individual phase shifters may fail in operation, it is necessary to maintain a reserve of similar phase shifters.